U.S. Pat. No. 4,053,167 discloses a sealing device for sealing between a screw and a nut, particularly of the ball screw type. The sealing device shown in the patent is mounted between a screw and nut and has a projection and ribs on its inner surface to seal against the screw thread. It is satisfactory for low fluid pressures such as up to about 500 psi. However, it may not always be satisfactory for high pressures because it utilizes a solid block of elastomeric material that seals against the nut and does not utilize fluid pressure to aid in such sealing.